This invention relates to diamond, and more particularly to diamond produced by chemical vapour deposition (hereinafter referred to as "CVD"), which is suitable for use as an insert for abrasive tools.
Methods of depositing material such as diamond on a substrate by CVD are now well established and have been described extensively in the patent and other literature. Where diamond is being deposited on a substrate, the method generally involves providing a gas mixture which, on dissociation, can provide hydrogen or a halogen (e.g. F,Cl) in atomic form and C or carbon containing radicals and other reactive species, e.g. CH.sub.x, CF.sub.x wherein x can be 1 to 4. In addition oxygen containing sources may be present, as may sources for nitrogen, and for boron. In many processes inert gases such as helium, neon or argon are also present. Thus, a typical source gas mixture will contain hydrocarbons C.sub.x Y.sub.y, wherein x and y can each be 1 to 10, halocarbons C.sub.x Y.sub.y Hal.sub.z (e.g. CF.sub.4), or CO.sub.x, wherein x can be 1 to 3 and optionally one or more of the following: O.sub.2, H.sub.2, N.sub.2, NH.sub.3, B.sub.2 H.sub.6, and an inert gas. Each gas may be present in its natural isotopic ratio, or the relative isotopic ratios may be artificially controlled; for example hydrogen may be present as deuterium or tritium, and carbon may be present as .sup.12 C or .sup.13 C. Dissociation of the source gas mixture is brought about by an energy source such as microwaves, lasers, RF energy, a flame, or a hot filament, and the reactive gas species so produced are allowed to deposit onto a substrate and form diamond.
Layers of CVD diamond have been proposed as inserts for abrasive tools, particularly cutting tools. CVD diamond layers have found limited commercial favour for such applications. One of the reasons for this is that CVD diamond layers have poor electrical conductivity making them difficult to cut and shape into a desired form for cutting insert using conventional EDM techniques. It has been proposed to introduce boron dopant atoms into CVD diamond layers to improve the electrical conductivity, but this has led to a deterioration in the strength of the layer.